This invention relates to an improved method and apparatus for separating carbon dioxide snow from a mixture of carbon dioxide snow and vapor.
When liquefied carbon dioxide flows through a restriction in a conduit such that the pressure of the liquefied carbon dioxide is reduced from a pressure above the triple point pressure (approximately 75 psia) to a pressure below the triple point pressure, the liquefied carbon dioxide is converted to a mixture of snow and vapor. In many practical applications, as where carbon dioxide snow is to be employed as a refrigerating medium and carbon dioxide vapor is to be recovered and removed from the presence of operating personnel and recycled, it is necessary to separate carbon dioxide snow from the mixture.
By way of background, U.S. Pat. No. 3,757,367, to Campbell, issued Sept. 11, 1973, entitled "Method for Carbon Dioxide Snow Separation" and assigned to the assignee of the present application which is incorporated herein by reference, teaches an apparatus and method for carbon dioxide snow separation. In such an apparatus a flowing mixture of carbon dioxide snow and vapor is first formed from liquid carbon dioxide, and then introduced through one end of a tubular conduit, curved to define a curvilinear flow path axially through the tubular conduit, such that carbon dioxide snow tends to be concentrated in a stream flowing axially through the tubular conduit. The concentrated stream of carbon dioxide snow is deflected from the remainder of the mixture and discharged from the tubular conduit. The patentee teaches that the pressure within the inlet end portion of the tubular conduit should be maintained between 5 and 60 psig. The patentee also teaches that this apparatus is capable of recovering approximately 38% of the liquid carbon dioxide as carbon dioxide snow, whereas the theoretical percentage of snow formed is 48%. The apparatus thus recovers approximately 79% of the snow that is present in the flowing mixture of carbon dioxide snow and vapor, thus the utility of the remaining 21% of the snow is being lost.
From the foregoing, it is apparent that there remains a need for an improved method and apparatus for efficiently separating carbon dioxide snow from a mixture of carbon dioxide snow and vapor.
It therefore becomes an object of this invention to provide an improved method and apparatus for efficiently separating carbon dioxide snow from a mixture of carbon dioxide snow and vapor. Other objects will become apparent from the following description of the invention.